The present invention relates to a method and apparatus for alarming decrease in tire air-pressure and a program for alarming decrease in tire air-pressure. More particularly, it relates to a method and apparatus for alarming decrease in tire air-pressure and a program for alarming decrease in tire air-pressure with which it is possible to improve the detection accuracy without issuing an erroneous alarm even in the case where a large driving force is applied when the vehicle is, for instance, running on a climbing road or when it performs trailer towing.
While various methods for detecting decompression of a tire attached to a vehicle have been suggested so far, the applicant of the present invention suggests a method for detecting decompression in which judgment of decrease in air-pressure can be performed by using a “turning correction logic” also during turning movements of the vehicle (see Japanese Unexamined Patent Publications No. 8713/1994 and No. 8714/1994).
According to the methods for detecting decompression as recited in Japanese Unexamined Patent Publications No. 8713/1994 and No. 8714/1994, decompression of a tire is detected upon comparing angular velocity signals from wheel speed sensors attached to each wheel. More particularly, wheel speed sensors composed of gearings provided with a magnetic pickup are employed for measuring respective wheel speed values C1, C2, C3 and C4 of the four wheels, and these values C1, C2, C3 and C4 are substituted into the following equation (1) for obtaining an error value DEL′.
                                                                        DEL                ′                            =                                                [                                                                                    (                                                  C1                          +                          C4                                                )                                            /                      2                                        -                                                                  (                                                  C2                          +                          C3                                                )                                            /                      2                                                        ]                                ×                                  100                  /                                                                                                                        [                                                      (                                          C1                      +                      C2                      +                      C3                      +                      C4                                        )                                    /                  4                                ]                            ⁢                                                                                                      (        1        )            
The error value DEL′ is then substituted into the following equation (2) for the “turning correction logic” for obtaining a corrected error value DEL.
                                                        DEL              =                                                DEL                  ′                                -                                  LAT                  ×                                      A                    (                                          ≈                                                                        DEL                          ′                                                -                                                  lateral                          ⁢                                                                                                          ⁢                          G                          ×                                                                                                                                                                                            (                                                correction                  ⁢                                                                          ⁢                  coefficient                  ⁢                                                                          ⁢                  1                                +                                  slip                  ⁢                                                                          ⁢                  rate                  ×                                                                                                                                                              correction                    ⁢                                                                                  ⁢                    coefficient                    ⁢                                                                                  ⁢                    2                                    )                                )                            ⁢                                                                                                      (        2        )            
When it is detected that the corrected value falls within a range of a specified threshold of 0.05 to 0.5, a tire alarm indicator within the vehicle is actuated for indicating that at least one tire has been detected.
However, where a large driving force is required, for instance, when running up a steep climb or when performing trailer towing, it would happen that such corrections could not be sufficiently performed particularly in the driving wheels so that erroneous alarm was apt to happen.
One possible factor thereof might be that a large slip is generated at the tire upon application of large driving force during turning movements so that corrections cannot be sufficiently performed by the above equation for turning correction alone.